Analyses of Wheat Yellow Rust Populations Reveal Sexual Recombination and Seasonal Migration Pattern of Puccinia striiformis f. sp. tritici in Gangu, Northwestern China.

Puccinia striiformis f. sp. tritici is the causal agent of wheat yellow rust with records of regular and severe epidemics in China. This study explored the population dynamics of the yellow rust pathogen in Gangu, northwestern China. In Gangu, the Weihe River runs from west to east and divides Gangu into three regions: North and South mountain, with the valley in between. To study the genetic structure of the pathogen in local populations, samples were collected over 3 years from the three regions at different altitudes both within and between the wheat cropping seasons. A total of 811 P. striiformis f. sp. tritici isolates were successfully genotyped using 16 simple sequence repeat markers. The results suggest that P. striiformis f. sp. tritici can survive year-round in Gangu. The P. striiformis f. sp. tritici populations migrated among the regions, and the migration pattern was not related to altitude. The oversummering populations in the North and South mountain regions were genetically different from each other; and the P. striiformis f. sp. tritici populations collected from the lower altitude in the valley had no relationship with any of the populations collected in the spring or fall, indicating that they too have a different origin. Signatures of random mating were found in the populations collected in both North and South mountain regions, but not in the valley populations.

Wheat Stripe Rust Epidemic and Virulence of Puccinia striiformis f. sp. tritici in China in 2002.

In China, wheat stripe rust, caused by Puccinia striiformis f. sp. tritici, is one of the most destructive diseases of wheat and can cause severe yield losses when susceptible cultivars are grown and weather conditions are favorable for the disease. Wheat stripe rust most frequently affects the winter wheat growing areas in Northwest, Southwest, and North China, and the spring wheat growing areas in Northwest China. In the 2001-2002 growing season, a widespread stripe rust epidemic affected about 6.6 million hectares of wheat in 11 provinces: Si-chuan, Chongqing, eastern Gansu, southern and western Shaanxi, southern and central Ningxia, Yunnan, Guizhou, Hubei, Henan, southern and central Hebei, and Shandong. The epidemic could be attributed to relatively warm weather from November 2001 to March 2002, high frequencies of stripe rust races CYR31 and CYR32, and widely grown susceptible cultivars. Race CYR31 was virulent on the Chinese differential cultivars Trigo Eureka, Fulhard, Lutescens 128, Mentana, Virgilio, Abbondanza, Early Premium, Funo, Danish 1, Fengchan 3, Lovrin 13, Shui-yuan 11, Lovrin 10, and Hybrid 46. Race CYR32 had all the virulence factors of CYR31, plus virulences on Chinese differential cultivars Jubilejina 2 and Kangyin 655, i.e., CYR32 was virulent on all differential cultivars, except Zhong 4. When tested on the world and European differential and some other resistant genotypes, CYR32 was virulent on Chinese 166 (Yr1), Heines VII (Yr2, Yr25, and YrHVII), Vilmorin 23 (Yr3a and Yr4a), Heines Kolben (Yr6 and YrHK), Lee (Yr7, Yr22, and Yr23), Clement (Yr9, Yr25, YrCle), VPM1 (Yr17), Selkirk (Yr27), Anza (YrA), Carstens V (YrCV1, YrCV2, and YrCV3), Gaby (YrG), Strubes Dickkopf (Yr25), and Suwon 92/Omar (YrSO). Resistance genes in Triticum spelta album (Yr5), Zhong 4, and Moro (Yr10 and YrMor) were effective against all races identified.